Warts are typically small, rough, and hard growths that are similar in color to the rest of the skin.[1][3] They typically do not result in symptoms except when on the bottom of the feet where they may be painful.[3] While they usually occur on the hands and feet they can also affect other locations.[1] One or many warts may appear. They are not cancerous.[3]

Without treatment, most types of warts resolve in months to years. A number of treatments may speed resolution including salicylic acid applied to the skin and cryotherapy. In those who are otherwise healthy they do not typically result in significant problems.[1] Treatment of genital warts differ from that of other types.[3]

Warts are very common with most people being infected at some point in time.[2] The estimated current rate of non-genital warts among the generally population is 1–13%. They are more common among young people.[1] Estimated rates of genital warts in sexually active women is 12%.[5] Warts have been described at least as far back as 400 BC by Hippocrates.[4]

Warts are caused by the human papilloma virus (HPV). There are about 130 known types of human papilloma viruses.[8] HPV infects the squamous epithelium, usually of the skin or genitals, but each HPV type is typically only able to infect a few specific areas on the body. Many HPV types can produce a benign growth, often called a "wart" or "papilloma", in the area they infect. Many of the more common HPV and wart types are listed below.

There are many treatments and procedures associated with wart removal.[17] A review of clinical trials of various cutaneous wart treatments concluded that topical treatments containing salicylic acid were more effective than placebo.[18]Cryotherapy appears to be as effective as salicylic acid, but there have been fewer trials.[18]

Two viral warts on a middle finger, being treated with a mixture of acids (like salicylic acid) to remove them. A white precipitate forms on the area where the product was applied.

This image shows throat warts (papillomas) before treatment and during the treatment process. Left to right: warts prior to treatment, warts on day of silver nitrate treatment, warts two days after treatment, warts four days after treatment, warts six days after treatment, and warts remaining nine days after treatment.

Salicylic acid can be prescribed by a dermatologist in a higher concentration than that found in over-the-counter products. Several over-the-counter products are readily available at pharmacies and supermarkets of roughly two types: adhesive pads treated with salicylic acid, and bottled concentrated salicylic acid solution.

Cantharidin, found naturally in the bodies of many members of the beetle family Meloidae, causes dermal blistering. It is used either by itself or compounded with podophyllin. Not FDA approved, but available through Canada or select US compounding pharmacies.

Dinitrochlorobenzene (DNCB), like salicylic acid, is applied directly to the wart. Studies show this method is effective with a cure rate of 80%. But DNCB must be used much more cautiously than salicylic acid; the chemical is known to cause genetic mutations, so it must be administered by a physician. This drug induces an allergic immune response resulting in inflammation that wards off the wart-causing virus.[22]

Another product available over-the-counter that can aid in wart removal is silver nitrate in the form of a caustic pencil, which is also available at drug stores. In a placebo-controlled study of 70 patients, silver nitrate given over nine days resulted in clearance of all warts in 43% and improvement in warts in 26% one month after treatment compared to 11% and 14%, respectively, in the placebo group.[24] The instructions must be followed to minimize staining of skin and clothing. Occasionally pigmented scars may develop.

Several randomized, controlled trials have found that zinc sulfate, consumed orally, often reduces or eliminates warts.[25][26][27] The zinc sulfate dosage used in medical trials for treatment of warts was between 5 and 10 mg/kg/day. For elemental zinc, a lower dosage of 2.5 mg/kg/day may be appropriate as large amounts of zinc may cause a copper deficiency.[25] Other trials have found that topical zinc sulfate solution[28] or zinc oxide[29] are also effective.

A 2014 study indicates that lopinavir is effective against the human papilloma virus (HPV). The study used the equivalent of one tablet twice a day applied topically to the cervices of women with high-grade and low-grade precancerous conditions. After three months of treatment, 82.6% of the women who had high-grade disease had normal cervical conditions, confirmed by smears and biopsies.[30]

Studies of fat-soluble garlic extracts have shown clearing in greater than 90% of cases. The extract is applied twice daily and covered with an adhesive bandage. Improvements show within 2–4 weeks and total clearing in an average of 6–9 weeks.[31][32][33]

Keratolysis, of dead surface skin cells usually using salicylic acid, blistering agents, immune system modifiers ("immunomodulators"), or formaldehyde, often with mechanical paring of the wart with a pumice stone, blade etc.[34]

Cryosurgery or cryotherapy, which involves freezing the wart (generally with liquid nitrogen),[36] creating a blister between the wart and epidermal layer after which the wart and the surrounding dead skin fall off. An average of 3 to 4 treatments are required for warts on thin skin. Warts on calloused skin like plantar warts might take dozens or more treatments.[20]

Laser treatment – often with a pulse dye laser or carbon dioxide (CO2) laser. Pulse dye lasers (wavelength 582 nm) work by selective absorption by blood cells (specifically hemoglobin). CO2 lasers work by selective absorption by water molecules. Pulse dye lasers are less destructive and more likely to heal without scarring. CO2 laser works by vaporizing and destroying tissue and skin. Laser treatments can be painful, expensive (though covered by many insurances), and not extensively scarring when used appropriately. CO2 lasers will require local anaesthetic. Pulse dye laser treatment does not need conscious sedation or local anesthetic. It takes 2 to 4 treatments but can be many more for extreme cases. Typically, 10–14 days are required between treatments. Preventative measures are important.[20]

Infrared coagulator – an intense source of infrared light in a small beam like a laser. This works essentially on the same principle as laser treatment. It is less expensive. Like the laser, it can cause blistering pain and scarring.[37]

Duct tape occlusion therapy involves placing a piece of duct tape over the wart. The mechanism of action of this technique still remains unknown. Despite several clinical trials, evidence for the efficacy of duct tape therapy is inconclusive.[38] Despite the mixed evidence for efficacy, the simplicity of the method and its limited side-effects leads some researchers to be reluctant to dismiss it.[39]

A variety of traditional folk remedies and rituals claim to be able to remove warts.

The acrid yellow sap of Greater Celandine is used as a traditional wart remedy.[40] The sap can be applied directly to the wart in a similar manner to concentrated salicylic acid solution, but in more modest quantities.

In The Adventures of Tom Sawyer, Mark Twain has his characters discuss a variety of such remedies. Tom Sawyer proposes "spunk-water" (or "stump-water", the water collecting in the hollow of a tree stump) as a remedy for warts on the hand. You put your hand into the water at midnight and say:

You then "walk away quick, eleven steps, with your eyes shut, and then turn around three times and walk home without speaking to anybody. Because if you speak the charm's busted." This is held to be superior to Huckleberry Finn's preferred remedy which involved throwing a dead cat into a graveyard. Another remedy involved splitting a bean, drawing blood from the wart and putting it on one of the halves, and burying that half at a crossroads at midnight. The theory of operation is that the blood on the buried bean will draw away the wart.[41] Twain is recognized as an early collector and recorder of genuine American folklore.[42]

Similar practices are recorded elsewhere. In Louisiana, one remedy for warts involves rubbing the wart with a potato, which is then buried; when the "buried potato dries up, the wart will be cured".[43] Another remedy similar to Twain's is reported from Northern Ireland, where water from a specific well on Rathlin Island is credited with the power to cure warts.[44]

A longstanding tradition holds that touching toads will cause warts. The most common Northern Hemisphere toads have glands that protrude from their skin that superficially resemble warts. Warts are caused by a virus, and toads do not harbor it.[45]